Investigations of laser-sustained plasma and its role in laser nitriding of titanium

Abstract

Laser-sustained plasma (LSP) and CCD imaging of reactant species were employed to investigate the role of near-surface plasma in CO2 laser nitriding of titanium in open atmosphere. Insights were gained regarding the role of plasma processes and the role of reactive nitriding species in the nitriding process. Studies of single nitrided trails have identified the following regimes, as a function of LSP off-focal distance and beam translation speed, characterized by (1) the formation of heavily oxidized surfaces, (2) the formation of titanium nitride (TiN) nanoparticulate, (3) nitride formation in the absence of a surface-struck or LSP and (4) the formation of near-stoichiometric, oxide-free TiN surfaces with a LSP. For the first time it will be shown that the LSP can access nitriding conditions beyond those achieved with surface-struck plasma (or in the absence of plasma) to produce uniform, near-stoichiometric, titanium nitride coatings.

Plasma column and nano-powder generation from solid titanium by localized microwaves in air

“…The continuum radiation in the 420-440 and 580-620 nm ranges may also indicate the presence of titanium in the form of titanium nitride (TiN). [48][49][50] The 750-780 nm range reveals the titanium oxidation according to the c-system band emission (A 3 U À X 3 D) from the TiO molecule. 49 The titanium plasma-column was also investigated by SAXS.…”

Laser-Sustained Plasma (LSP) Nitriding of Titanium: A Review

“…The role played by near-surface plasma during CW CO 2 laser nitriding of commercially pure titanium (CP-Ti) was investigated in great detail in the Center for Multi-scale Wave-Material Interaction (CMWMI) at the Pennsylvania State University [100,106,[108][109][110][111][112] in recent years, resulting in the development of the so-called "LSP nitriding" process that was capable of improving the wear resistance of CP-Ti in open and uncontrolled atmosphere with minimal surface oxidation. Using a combination of charge-couple device (CCD) imaging and optical spectroscopy, Nassar et al [108] characterized the near-surface plasma formed during the laser nitriding process as a function of scanning speed and off-focal distance (OFD). They found three main processing regimes pertinent to plasma formation:…”

“…Finally, at high scan speeds and/or large OFD's, near-surface titanium plasma was not observed. Nassar et al [108] thus found a processing window of scan speeds and OFD's (Regime 2) where a nitrogen-rich near-surface plasma struck during laser nitriding CP-Ti. Further, using X-ray photoelectron spectroscopy (XPS), Nassar et al [108] observed that nitriding in the presence of nitrogen-rich plasma (Regime 2) in an open and uncontrolled atmosphere reduced surface oxidation in the nitrided layers, which was attributed to the gettering action of the plasma whereby the active nitrogen species reacted with atmospheric oxygen.…”

“…Nassar et al [108] thus found a processing window of scan speeds and OFD's (Regime 2) where a nitrogen-rich near-surface plasma struck during laser nitriding CP-Ti. Further, using X-ray photoelectron spectroscopy (XPS), Nassar et al [108] observed that nitriding in the presence of nitrogen-rich plasma (Regime 2) in an open and uncontrolled atmosphere reduced surface oxidation in the nitrided layers, which was attributed to the gettering action of the plasma whereby the active nitrogen species reacted with atmospheric oxygen. Additionally, microstructural characterization of the nitrided layers revealed no evidence of energy attenuation of the laser beam in the presence of Nassar et al [108] thus found a processing window of scan speeds and OFD's (Regime 2) where a nitrogen-rich near-surface plasma struck during laser nitriding CP-Ti.…”

“…Further, using X-ray photoelectron spectroscopy (XPS), Nassar et al [108] observed that nitriding in the presence of nitrogen-rich plasma (Regime 2) in an open and uncontrolled atmosphere reduced surface oxidation in the nitrided layers, which was attributed to the gettering action of the plasma whereby the active nitrogen species reacted with atmospheric oxygen. Additionally, microstructural characterization of the nitrided layers revealed no evidence of energy attenuation of the laser beam in the presence of Nassar et al [108] thus found a processing window of scan speeds and OFD's (Regime 2) where a nitrogen-rich near-surface plasma struck during laser nitriding CP-Ti. Further, using X-ray photoelectron spectroscopy (XPS), Nassar et al [108] observed that nitriding in the presence of nitrogen-rich plasma (Regime 2) in an open and uncontrolled atmosphere reduced surface oxidation in the nitrided layers, which was attributed to the gettering action of the plasma whereby the active nitrogen species reacted with atmospheric oxygen.…”